POLAR ICE NOT DUE TO ELEVATION. 71 



during the heat of summer becomes partially melted 

 and refrozen into compact ice; while the intervening 

 white portions represent the snow of the greater part 

 of the year, which of course would become converted 

 into ice without ever being actually melted. It is, 

 therefore, more than probable that each bed with its 

 corresponding blue band may represent the formation 

 of one year. Judging from the number of these layers 

 in an iceberg, some of these bergs must be of immense 

 age, occupying a period probably of several thousand 

 years in their formation. And as the ice is in a con- 

 stant state of motion outwards from the centre of 

 dispersion — probably the South Pole — the bergs before 

 becoming detached from their parent mass must have 

 traversed a distance of hundreds of miles. 



The fact that these bergs must have travelled from 

 great distances in the interior is further evident from 

 the following consideration. The distance between the 

 well-marked blue lines is greatest near the top of the 

 berg, where it may be a foot or more, and becomes less 

 and less as we descend, until, near the surface of the 

 water, it is not more than two or three inches. This 

 diminution in the thickness of the ice-strata from the 

 top downwards has been considered by Sir Wy ville to 

 be mainly due to two causes — compression, and melting 

 of the ice, particularly the latter. But in my paper on 

 the Antarctic Ice ("Quart. Journ. of Science," Jan. 1879) 

 I have shown that, although compression and melting 

 may have had something to do in the matter, this 

 thinning of the strata from the top downwards is a 

 necessary physical consequence of continental ice 

 radiating from a centre of dispersion. Assuming the 

 South Pole to be this centre, a layer which in, say, 

 latitude 85° covers 1 square foot of surface will, on 

 reaching latitude 80°, cover 2 square feet; at latitude 



